Talvivaara Mining Company has developed a proprietary bioheap leaching technology for extracting valuable metals such as nickel, copper, cobalt, and zinc from sulphidic ore or waste materials. The method is both cost-effective and environmentally friendly.
Biology is opening up exciting new frontiers in mining, and 'bugs' can be expected to play a growing role in the low-cost, efficient, and clean discovery, extraction, and processing of minerals as the twenty-first century progresses.
|Irrigation tubing on the surface of a bioheap.
In general, microbes extract minerals by oxidising ferrous iron to ferric iron, and sulphur to sulphates. This generates oxidising conditions that dissolve the target metals in a mineral out of the ore into a solution, from which it can then be recovered using conventional methods.
Talvivaara Mining has taken this basic principle and developed a new bioheap leaching process to create and maintain the ideal environment for this type of bacterial activity through careful heap design and the efficient management of internal heap parameters, such as temperature, aeration, water, nutrients, and acid balance.
Getting the parameters right
A variety of microbial populations need to be present over time, and their growth rates need to be optimum, to reach and maintain the temperatures required for enhanced primary sulphide mineral leaching. As temperatures need to be well in excess of 50 °C for successful bioleaching, the mesophile population required for early heat generation needs to be replaced by a thermophile population for sustained heat generation at the appropriate point.
Factors such as micro-organism dynamics, adaptation and succession rates, as well as ore energy-generating capacity, all need to be addressed. Optimising the rate of leaching and understanding what can inhibit or retard microbial growth are also important.
Get all of this right, and the result can be very valuable in terms of enhanced economics.
Better for the environment
In addition to attractive cost benefits, bioheap leaching also offers significant environmental advantages, as bacteria consume carbon dioxide and convert it into organic material that can be returned to the carbon cycle. The bio-oxidation of sulphide minerals generates no noxious gases, as all the sulphides are converted into water-soluble sulphates.
As any exposed sulphide mineral or deposit close to the surface will undergo natural weathering via bacterial attack, there are clear benefits to oxidising these minerals in a controlled fashion and preventing acids and metals leaching into the water table and soil. Bioheap leaching produces metal ions, acid, and inert rock devoid of sulphide mineralisation. Metals can be removed by electrolysis and/or precipitation, and any acid generated collected for neutralisation.